“All ports in the Bay Area will be shut down to protest the atrocity of Johannes Mehserle killing Oscar Grant,” Heyman said. “We intend to send a message loud and clear to the powers that be. Cops have to go to jail when they commit a crime just like anyone else.”

Union workers said they received permission from the Pacific Maritime Association to move their monthly “stop work” meeting from Thursday to Saturday.

Marilyn Sandifur, a spokeswoman for the Port of Oakland, said she does not expect the protest to significantly affect cargo operations.

“We will see what happens when millions of dollars of cargo remain idle,” said Heyman, who estimates some 4,000 dock workers will not be working for eight hours on Saturday.

The 1,300-member union decided to hold the rally after a meeting with Grant’s uncle and Jack Bryson, whose sons were with Grant when he was killed.

Since Mehserle’s conviction, several rallies have been held supporting him.

A sailboat with an American flag and a “Free Johannes Mehserle” banner, organized by his father, has plied waters outside the San Francisco Giants baseball stadium and shown during nationally televised playoff games.

At least two boats featuring banners mentioning Grant also have appeared nearby.